We have recently isolated and partially characterized four distinct dsDNA viruses which replicate in Chlorella-like green algae symbiotic with Hydra and Paramecium. Attempts to infect a number of cultured Chlorella strains with the four viruses revealea that one of the viruses, PBCV-1, replicated in two of the Chlorella strains. This has allowed the production of mg quantities of a eukaryotic virus as well as the development of abiological (plaque) assay for PBCV-1. The PBCV-1 Chlorella system is the first example of a virus infecting any eukaryotic plant which can utilize procedures directly adapted from those used to study bacteriophage. The objectives of this proposal are to investigate the structural organization of the large viral genome (ca. 280 kbp) and the nature and function of the viral gene products. Using established methods we intend to (i) characterize the dsDNA genome, (ii) attempt to infect algal protoplasts with isolated PBCV-1 DNA, (iii) prepare a restriction map of the genome, (iv) monitor the synthesis of viral gene products during the viral replication cycle, and (v) isolate and characterize temperature sensitive mutants of PBCV-1. The research has several potentially important long range implications. Studies on PBCV-1 will: (i) provide an opportunity to study a new type of virus-host relationship, (ii) determine the role it plays in symbiosis, (iii) demonstrate the usefulness of PBCV-1 or PBCV-1 DNA as a vector for transferring genes into other algae or higher plants, and (iv) determine if PBCV-1 or PBCV-1 lysates contain a new source of plant cell wall degrading enzymes. Finally studies on the regulation and expression of the dsDNA viral genome in the host will provide new information on gene regulation in eukaryotic plants.